1. Field of the Invention
The present invention relates to a voltage regulator circuit, and in particular, to a circuit having a low quiescent current, and high stability at high temperatures.
2. Description of the Related Art
Voltage regulator circuits are found in most electronic devices in use today. Such circuits are configured to receive, at an input, an unregulated voltage supply, and to provide, at an output, a regulated voltage at a selected voltage level, lower than the input. Such circuits are commonly used, for example, in devices that are powered by batteries, in order to maintain a steady voltage supply for the device, even as the output voltage of the battery gradually drops due to normal discharge of the battery. Voltage regulator circuits are also found in systems requiring a voltage supply at one voltage level but where power is available at a different voltage level.
Voltage regulator circuits typically require some power to operate. For example, such circuits employ reference voltage generators, voltage sensing sub-circuits, and other sub-circuits that remain active while the regulator circuit is powered up, even when there is no load on the output. As a result, the regulator circuit will draw a current from the power supply, regardless of the load. This current is commonly referred to as the quiescent current.
In a battery operated system such as that described, the quiescent current represents a constant drain on the battery, as long as the system is active. Accordingly, it would be desirable, especially in a battery powered system, to turn off the regulator when there is no load present. However, this is not always possible. In some applications, it is necessary to maintain a voltage level at the output even while there is minimal current draw. For example, some systems maintain a clock, a volatile memory, or some other circuit that has negligible power requirements, but must have a continuous voltage supply. Such circuits are found, for example, in automobiles, where various systems remain nominally active, perpetually, even while the automobile is not in operation.
For example, a typical automobile audio system maintains a memory of radio settings, etc., which are stored in a volatile memory, such that if the power is disconnected the memory is erased. In addition, modern automobiles employ computers, which similarly must be kept powered to maintain data in memory. Each such system will employ a separate regulator circuit, such that the quiescent current draw on the battery may be multiplied many times. Some modern automobiles may include a dozen or more such systems.
In view of the above, it is desirable to reduce the quiescent current of each voltage regulator circuit, in order to minimize the drain that the sum of the quiescent currents represents on the battery.